--> ABSTRACT: Latest Proterozoic to Early Cambrian Sedimentary-Tectonic Evolution of a Passive Margin Sequence, Northeastern Washington, by Kevin A. Lindsey and David R. Gaylord; #91040 (2010)

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Latest Proterozoic to Early Cambrian Sedimentary-Tectonic Evolution of a Passive Margin Sequence, Northeastern Washington

Kevin A. Lindsey, David R. Gaylord

The late Proterozoic to Early Cambrian Three Sisters formation, Addy Quartzite, and Gypsy Quartzite lie near the base of the Cordilleran miogeocline in northeastern Washington. Detailed stratigraphic and sedimentary examination of these units extends understanding of the evolution of western North America. These units were deposited on a newly rifted passive margin and record the final stages of late Proterozoic rifting and the early stages of subsequent early Paleozoic subsidence and transgression. The Three Sisters formation, Addy Quartzite, and Gypsy Quartzite are correlative with the Brigham Group in southeastern Idaho and Utah, the Gold Creek Quartzite in northern Idaho, and the Flathead Quartzite in Montana and Wyoming.

Strata underlying the Three Sisters formation at the base of the miogeocline appear to have been deposited in intracratonic grabens that formed cratonward (east) of the main locus of rifting. The lower Three Sisters formation was deposited under restricted basin conditions in one of these intracratonic grabens toward the end of rifting. The upper Three Sisters formation was deposited in braided fluvial and alluvial fan delta settings as the graben filled.

Subsidence of the continental margin during the waning stages of rifting promoted cratonward transgression. The Addy and Gypsy Quartzites were deposited in braided fluvial, beach, nearshore, shoreface, and inner shelf settings along the leading edge of this transgressing sea. Deposition of these quartzite units in northeastern Washington ceased as the continental margin continued to subside. Subsequently, the deeper water argillites and limestones of overlying units were deposited in outer shelf and shelf-edge settings.

AAPG Search and Discovery Article #91040©1987 AAPG Rocky Mountain Section Meeting, Boise, Idaho, September 13-16, 1987.